Screen for digesters



June 29, 1939. W RICHMOND 2,163,437

SCREEN FOR DIGESTERS V Filed Feb. 24, 1936 2 Sheets-Sheet 1 f g? I FF. j.

WwWA WA 4 7- TUR/VE/ June 20, 1939. H. R D 2,163,437

SCREEN FOR DIGESTERS Filed Feb. 24, 1936 2 Sheets-Sheet 2 H1 //\/A/E/\/ 727 H. H- RICHMOND A TTUFQ/VE Patented June 20, 1939 UNITED STATES PATENT OFFlCE Electric Steel Foundry Company, Portland,

Oreg., a corporation of Oregon Application February 24, 1936, Serial No. 65,319

1 Claim.

This invention relates generally to the paper making art and particularly to a screen for digesters.

The main object of this invention is the provision of an improved form of screen for digesters having an extra large screen area.

The second object is the construction of a screen for digesters which will offer little or no resistance to the discharge of the contents of the digester when it is drained from the bottom.

The third object is the construction of a screen with an improved means for supporting same within the digester in a manner to make same unaffected by the various rates of expansion in the various elements thereof.

I accomplish these and other objects in the manner set forth in the following specification as illustrated in the accompanying drawings, in

which:

Fig. 1 is a fragmentary vertical section through a digester showing the location of the screen.

Fig. 2 is a section taken along the line 22 in Fig. 1.

Fig. 3 is a section taken along the line 3-3 in Fig. 4.

Fig. 4 is a fragmentary elevation of a screen plate showing the holes formed therein.

Fig. 5 is a section taken along the line 5-5 in Fig. 6.

Fig. 6 is a section taken along the line B-6 in Fig. 2. showing the preferred form of cast section.

Fig. '7 is a section taken along the line 'I-l in Fig. 6.

Fig. 8 is a view similar to Fig. 6, showing an alternate form of cast section.

Fig. 9 is a section taken along the line 9-43 in Fig. 8.

Fig. 10 is a view similar to Fig. 8 showing a still further modification combining cast and plate sections for the screen.

Fig. 11 is a section taken along the line lI-ll in Fig. 10.

Fig. 12 is a section taken along the line I2-|2 in Fig. 10.

Similar numbers of reference refer to similar parts throughout the several views.

Referring in detail to the drawings, there is shown a common form of digester I4 provided with a brick lining l5 and the domed head it. It will be understood that these digesters are employed to subject wood chips to the action of a digesting acid in the presence of heat for the purpose of breaking down the chips into a fibrous mass. The liquor is drawn off through a pipe I! under the control of a valve IS. The difficulty normally encountered in such drawing off process lies in the fact that the chips and fibers themselves serve as a screen so that if a screen is merely placed over the end of the pipe ll, its fiow soon becomes so obstructed as to seriously 5 retard the drawing off action. It is therefore the purpose of this invention to so construct the screen that its capacity will be so large that no objectionable restriction will be offered to the flow of liquor through the pipe ll.

Referring particularly to the invention, same will be seen to consist of a circular screen I9 which is disposed Within the cylindrical wall of fire brick l5 as shown in Fig. 1. In its preferred form, as shown in Fig. 6, the screen l9 has its intermediate portion 20 substantially vertical and spaced from the lining plate 2!, while the lower side 22 and the upper side 23 converge toward the plate 2|. Angle bars 24 are employed to hold the edges of the sides 22 and 23 against the plate 2! by means of the bolts 25. The portions 2t], 22, and 23 are integral with each other and are preferably reinforced by means of the ribs 26. The ribs 2'! are provided on the sides 22, and the bolts '28 extend through the ribs 21 for the purpose of uniting the various sections.

Fig. 8 illustrates an alternative form of cast section employing a smaller rib 29 with reinforcements 3!} at the inner corners of the screen. The ribs 3| are provided on the lower side 32 for the fastening bolts 33. In this form of the section, the angle bars 3 1 are on the outer side of the screen instead of on the inner side. This expedites somewhat the flushing of the digester.

In the form. of the device illustrated in Fig. 10 is combined a cast frame which includes the ribs 35 and tie bars 36, across the latter of which are mounted the perforated screen plate sides 31, 38, and 39. The entire screen is held in position by means of the angle bars 24. 40

The individual screen plates 26, 22, 23, 32, 31, 38, and 39 are preferably constructed as shown in Figs. 3 and 4, that is, with the tapering openings M] with the larger end of each opening toward the outside of the digester [4. One or more pipes l1 communicate with the space M around the screen.

In the form of the screen shown in Figs. 10, 11 and 12, the screen plates 38 do not form a cylinder but a polygon of many sides. The plates 38 rest upon the grill formed by the ribs 35 and the tie bars 36. The bars 36 are bent at the points 42 as shown in Fig. 11, which places corresponding bends at the contacting edges 43 of the plates 38. It will also be noted that the edges 44 of the grill meet at the center line of the perforated plate 38. Along the lower edge of the plate side 39 and the upper edge of the plate side 40 are placed the clamp bars 45, which are held in place by the bolts 46.

It can be seen from the foregoing that the screen area has been increased to such an extent that there is no appreciable restriction to the passage of the fluid through the holes 40.

Owing to the frequent changes in temperature through a wide range and the consequent variations in the expansion and contraction of the various elements involved and also the turbulent action set up within the digester itself while the cooking action is taking place, it is a relatively difficult matter to hold a screen of this character in an operable position. However, by the use of the structure herein illustrated and described, no difiiculty is experienced in holding the screen plates in their proper positions, and consequently, no difiiculty is experienced in satisfactorily screening the liquor from the digester.

The construction herein illustrated also has the advantage of lending itself to various kinds of manufacture, that is to say, it may be made of all cast elements, or of combined cast and wrought, or of all wrought sections without departing from the spirit of this invention.

While reference has been made to the use of perforated plates, it must, of course, be understood that a suitable wire cloth may also be employed without departing from the spirit of this invention.

I claim:

A screen for digesters consisting of a plurality of arcuate, perforated, channel-shaped screen sections adapted to be united into a complete circular screen whose outermost edges conform to the diameter of the interior of a digester, the intermediate portions of said screen having a smaller radius than do the upper and lower edges thereof, clamp members for holding the edges of said screen in a fixed position against the interior of the digester, and a valve controlled conduit communicating between the space existing between said screen and the digester Wall and with the interior of the digester, the total area of the perforations in said screen exceeding the cross sectional area of said conduit.

HARRY I-I. RICHMOND. 

